Photographic elements



Patented June 26, 1945 PHOTOGRAPHIC ELEMENTS Otis Willard Murray,

Metuchen, N. J assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 1, 1944, I

Serial No. 516,701

4 Claims.

This invention relates to novel photographic elements which have the photosensitive layer or layers thereof protected from exposure to visible light. More particularly it relates to such elements which are useful for obtaining X-ray photographs or radiograms. Still more particularly it relates to X-ray films which can be safely handled under conditions of ordinary room illumination without exposure of the photosensitive layers thereof.

Photographic elements with various types of antihalation layers have been proposed and manufactured commercially. In general they comprise a support, a light sensitive layer and an antihalation layer composed of a removable natural or synthetic material which has dispersed therethrough an antihalation or light absorbing dye or pigment. The light sensitive layer is placed on one side of the base and the antihala tion layer on the other. Various water soluble cellulose derivatives, and synthetic resins are among the substances which have been proposed. Materials which are soluble in dilute alcohol solutions or in alkaline developer solutions have also been advocated but they require special conditions for manufacturing or processing.

Photographic elements for obtaining X-ray photographs which are provided with an opaque protecting medium for the sensitive layer are known. The previous protective layers, however, were not entirely satisfactory for X-ray films because the layers are difilcult to remove after exposure to X-rays and the light-blocking material is not uniformly distributed throughout the layer.

This invention has for an object a photographic element for X-rays which can be handled under daylight conditions without exposure. A further object is such an element which is provided with antihalation layers which can be removed easily and completely in aqueous baths. A still further object is to provide such an lement wherein the antihalation layer is photographically inert and the light-blocking material is nondiifusing and uniformly dispersed throughout the layers.

The novel photographic elements for X-ray elements of this invention comprise a base having superposed thereon at least one photosensitive emulsion layer and two outer light absorbing protective layers disposed on the outer surfaces of the element. In the case of duplicoated X-ray film the elements comprise a film base or support having a photographic emulsion layer coated on each side of the base and a protective layer coated on each photographic emulsion layer which contains a nondifiusing light absorbing material.

The protective light-blocking or antihalation layers consist of an aqueous dispersion of a mixture of casein and gelatin and a black inert pigin'ent such as colloidal carbon or finely divided carbon black which is uniformly distributed therethrough. The casein and gelatin are present in the amount of 10 to 20 parts of the former per part of the latter. The amount of the black inert pigment particles may vary over a fairly wide range but should be present in suflicient amount that thin layers preventvisible light from penetrating therethrough and exposing the photographic layers. A particle size of 10 to 100 mu represents a practical range and 30 to 80 mu a preferred range for aforesaid pigments.

I The coating mixtures can be made in the form of an aqueous dispersion or paste and coated in a manner similar to that in which gelatinsilver halide emulsions are coated. They can be made by dispersing the colloidal silver or carbon or carbon black in an aqueous dispersion of gelatine and casein. Various wetting and dispersing-agents can be used in aiding the dispersions such as sodium alkyl sulfates at 10 to 18 carbon atoms lower alkyl (e. g. 1 to 4 carbon atoms) naphthalene sulfonic acid sodium or potassium salts, alkane sulfonic acid sodium salts having 10 to 18 carbon atoms, etc. Coating may be'accomplished by spreading, spraying, dipping, transfer or beading rollers, etc.

Various thicknesses of the antihalation layers may be formed but in general thicknesses of 15 to microns in thickness are sufficient. The thickness of the layer and amount of pigment should be controlled so that the resulting layer has a density of about4 to 7. I

The invention will be further illustrated but is not intended to be limited by the'following examples.

EXAMPLE I SolutionA Water cc 9100 Casein grams 1000 Sodium carbonate (10% aqueous solutlon) cc e 340 Solution B Colloidal carbon (particle size 50 mo.)

grams 1000 Water cc 2000 Sodium dodecyl sulfate solution) Solution C Gelatin grams- 100 Water cc 1250 Sodium dodecyl sulfate (10% aqueous solution) cc.. 100 Saponin (5% aqueous solution) cc 100 The mixture was coated onto each gelatin silver halide layer in the dark at about 90 C. to form 1 a layer approximately microns thick. The resulting layer after drying had a density greater than 4.0. No visible fog was produced after a 20 minute exposure in a normally lighted room but a slight edge fog developed, e. g., about inch around the periphery of the film. The black antihalation layer was removed easily after a three minute soak in water by gentle swabbing with cotton. Satisfactory radiographs were taken without cassettes or holders under ordinary room illumination and no loss of emulsion speed was noted.-

Exmu II A cellulose acetate film base having a thin coating of nitrocellulose on each side, was coated on each side with gelatin and then with a gelatin silver halide emulsion of the X-ray type after the manner of U. S. P. 1,947,160. On each emulsion surface was coated a thin layer (e. g.

Solution B was added to Solution A slowly and then Solution C was added and the resulting solution filtered. The composition was then coate d 40 media for the pigments used by this invention in darkness onto each of the emulsion layers of aforesaid film element to a thickness of 50 microns. The resulting element had a density of greater than 4. The layer was easily removed in the developing solution by a gentle swabbing with cotton.

Various commercialforms of colloidal carbon or carbon black which have a very fine particle size for instance from 10 to 100 millimicrons including mixtures of particles having sizes within these ranges can (e. g. 0.5 to 2% of the gelatin) of the cellulose derivatives described in such patents may also be present. The black inert pigments can be be substituted for those described in the above examples. Small amounts by weight of pigment to 20 parts of combined casein and gelatin to two parts of pigment to one part of combined gelatin and casein.

Additional useful wetting agents include alkali metal alkyl sulfates of 8 to 20 carbon atoms, e. g. sodium octyl sulfate. sodium tetradecyl sulfate. sodium hexadecyl sulfate, ammonium octadecyl sulfate, oleyl sulfate, sodium n-hexadecanesulfonic acid, tri-isopropylnaphthalene sulfonic acid the condensation products of ethylol cyanamides with lauric, stearic, palmitic, etc., acids.

By varying the proportion of casein to the photographic gelatin it is possible to modify the properties of the layers somewhat. The higher proportions, e. g. 15 to 20 of casein make the layers removable in a water rinse before development whereas somewhat lower proportions render the layers soluble in alkaline developer solution. Proportions near the lower limits render the layers removable near the end of normal development with gentle swabbing. Water rinses after development remove all traces of the products. It has been found that layers composed of casein alone are too brittle to be of use.

The antihalation elements of this invention as described above have all the desirable characteristics of a commercially practical element. Their preparation does not present any coating difllculties. The layers are soluble in aqueous treating baths and may be removed from the film by treatment in such baths. They are photographically inert and hence do not adversely affeet the radiation sensitive layers. The lightblocking pigments are non-diffusing and are uniformly dispersed throughout the combination colloid layer. In addition, the layers have excellent anchorage to gelatin layers and require no additional agents to'form an effective bond.

Various resins have been evaluated as binding but were found to be unsatisfactory. The resins did not provide a uniform and completely lightblocklng layer. Poor dispersions were obtained with those of the water soluble type.- Moreover the antihalation materials were not fast to diffusion. Thus it was found that water soluble cellulose derivatives, e. g. methyl cellulose and cellulose glycolate were inferior binding agents and were poor binding agents for colloidal carbon. The resins moreover are difficult to coat. These facts evidence that the novel elements of this invention have properties which are surprising and unexpected.

The invention provides a novel X-ray film which can be handled safely in diffused daylight or under ordinary room illumination but yet can be easily processed to X-ray photographs. They eliminate the use of cassettes and enable the technician to exercise much greater latitude and attain more speed in roentgenology. In addition, the layers are abrasion resistant, have good antistatic properties.'are not affected by changes in humidity and have good aging properties.

I claim;

1. A photographic element comprising a base. a light sensitive emulsion layer, a light-blocking outer antihalation layer disposed on each side of said element composed of casein and gelatin in -the proportion of 10 to 20 parts of the former per part of the latter having intimately and uniformly dispersed therethrough finely divided carbon particles.

2. A photographic element comprising a base, a light sensitive emulsion layer, a light-blocking used in a wide range of proportions e. g. one part 7 outer antihal tion layer disposed on each side of said element composed of casein and gelatin in the proportion of 10 to 20 parts of the former per part of the latter having intimately and uniformly dispersed therethrough colloidal carbon.

3 An X-ray film element comprising a transparent film base, a gelatin silver halide emulsion imposed on each side thereof and a light blocking antihalation layer superposed on each emulsion layer composed of casein and gelatin in the proportion of 10 to 20 parts of the former per part of the latter having finely divided carbon particles uniformly dispersed therethrough.

4. A11 X-ray film element comprising a transparent film base, a gelatin silver halide emulsion imposed on each side thereof and a light-blocking antihalation layer superposed on each emulsion layer composed of casein and gelatin in the proportion of 10 to 20 parts of the former per part of the latter having colloidal carbon possessing a particle size of 10 to 100 millimlcrons dispersed therethrough said layer having a phys- 10 ical density of from 4.0 to 7.00.

OTIS WILLARD MURRAY. 

